1. Technical Field
This invention relates generally to flame-retardant materials, and more particularly to extruded flame-retardant compounds and to their method of manufacture.
2. Related Art
It is known to manufacture fabrics from flame-retardant yarns, wherein the fabrics are used to protect items from exposure to flame. For example, it is known to construct braided, woven or knitted sleeves from fire-retardant yarns to protect elongate items, such as wires, contained within the sleeves. One known compound ingredient which has desirable fire-retardant properties is melamine cyanurate (MC).
The assignee herein is also the assignee of U.S. Pat. No. 6,828,365, wherein MC is compounded with a fire-retardant polyphosphonate filler and a polymer selected from the group consisting of poly(ethylene terephthalate) and poly(ethylene naphthalate) and then extruded to form a fire-retardant monofilament. Since polyphosphonate is fire-retardant as well, it provides the resulting monofilament with additional fire-retardant properties.
Current commercially available halogen-free flame-retardant poly(ethylene terephthalate) (FR-PET) is made by adding an organo-phosphorous compound in the polycondensation stage of the PET polymerization process, such as in U.S. Pat. No. 4,086,208, which is incorporated herein by reference in its entirety. Unfortunately, the flame-retardant properties of this phosphorus-containing PET (P-FR-PET) do not meet the most stringent flame test requirements. In particular, the burn time and flame spread distance are too long, and it emits flaming drips.